Assembly with metal casting and polymeric member and transmission shift mechanism

ABSTRACT

An assembly includes a polymeric member and a unitary metal casting. The metal casting is engaged with and relatively moveably capturing the polymeric member on the metal casting. The polymeric member includes an opening extending through the polymeric member. The opening defines a rotational axis of the polymeric member and includes a central cylindrical portion and first and second end portions having diameters greater than the central cylindrical portion. The first and second end portions are disposed proximate opposite ends of the opening, and the metal casting substantially fills the central cylindrical portion and the first and second end portions of the opening, thereby rotatably disposing and axially capturing the polymeric member on the metal casting. The assembly can be adapted for use as a crank arm in a transmission shift mechanism.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a Divisional Application of U.S. Non-Provisionalpatent application Ser. No. 13/115,592, filed May 25, 2011, which is aDivisional Application of U.S. Non-Provisional patent application Ser.No. 11/586,132, filed Oct. 25, 2006, both of which are incorporatedherein, by reference, in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an assembly including a metal castingand a polymeric member and, more particularly, such an assembly that issuitable for use in a transmission shift mechanism for a vehicle.

2. Description of the Related Art

Vehicles having an automatic transmission oftentimes have a shift levermounted on the steering column of the vehicle. Many of these mechanismshave an actuator-driving crank arm that includes an arm portioncomponent with a ball component mounted on the arm portion to providethe crank arm with a substantially spherically-shaped ball end. In someknown mechanisms, the ball component of the crank is rotatable relativeto its arm portion component while in other known mechanisms, the ballcomponent is fixed to the arm portion and cannot rotate relative to thearm portion.

In such known mechanisms, the ball component is often disposed within anarcuate cam slot opening located on a pivoting actuator. Rotationalmovement of the crank arm moves the actuator between various positionsabout its pivot point. One end of a cable or linkage is attached to theactuator with the other end being attached to the gear selector of thetransmission of the vehicle so that movement of the cable effectstransmission gear selection.

The arm portion of the crank arm is typically steel, and requiresmachining to form the crank arm from extruded bar stock to control sizetolerance and material consistency. The arm portion of such typicalcrank arms is generally manufactured from a steel rod in a progressive,cold forming stamping process that requires several separate formingand/or machining operations to yield the arm portion.

In a subsequent metal forming operation, the ball component of the crankarm is then attached, typically by being staked onto the stamping thatforms the arm portion. Generally, the staking process will fix the ballon the crank arm in a manner that does not allow the ball to rotaterelative the crank arm. The assembly process whereby the ball componentis assembled to the arm portion can produce scrap from over/understaking. Additionally, the staking of the ball sometime producesinconsistent positional tolerances and/or results in failure due to ballseparation.

The arm portion requires selective orientation at the next level ofassembly wherein the crank arm is attached to its rotatable shift shaft.The ball component is typically a self-lubricating plastic that has ashape formed by a machining process. When staking the ball component onthe portion to non-rotationally fix the ball on the crank arm, therotational position of the ball component is generally not controlledand, thus, the entire exterior surface of the ball must be preciselyformed, even though in operation a substantial portion of the ballexterior surface may never engage a surface of the actuator cam opening.

The use of a staking process that fixes the ball component on the armportion component without allowing the ball to rotate will generally beless expensive than attaching the ball component to the arm portion in amanner that allows the ball to rotate relative to the arm portion. Forexample, it is known to use a shoulder bolt to rotatably attach a ballcomponent. Ball components used to manufacture crank arms using astaking process are generally formed by machining an extruded plasticmaterial. By machining an extruded plastic material to the ball, thedimensions of the ball can be controlled. Moreover, a ball formed bymachining an extruded plastic material will have greater strength than asimilar ball formed by injection molding. The differential cooling of aninjection molded ball component will oftentimes reduce the strength ofthe ball near its exterior surface which, when non-rotatably staked tothe arm portion, is in sliding engagement with the cam slot. Althoughthe machining of extruded plastic material to form a ball component isgenerally more expensive than injection molding a ball component,injection molded ball components typically do not have the strengthnecessary to provide a durable and reliable product when placed insliding engagement with the camming slot. Thus, the ball component musttypically be formed using the relative more expensive process ofmachining an extruded material.

Accommodating the manufacturing and assembly-related factors of knownshift mechanism crank arms make such crank arms undesirably expensive.

SUMMARY OF THE INVENTION

The present invention provides an assembly having a polymeric membermoveably coupled with a metal casting and which can be adapted for useas a crank arm in a transmission mechanism.

The invention comprises, in one form thereof, an assembly including apolymeric member and a unitary metal casting wherein the metal castingrelatively moveably captures the polymeric member on the metal casting.

In some embodiments of the assembly, the polymeric member includes anopening defining a rotational axis of the polymeric member. The metalcasting extends into the opening and includes at least one enlargeddiameter portion with the polymeric member being rotationally disposedon the metal casting and axially captured on the metal casting by the atleast one enlarged diameter portion of the metal casting.

In some additional embodiments of the assembly, the polymeric memberincludes an opening that includes a central cylindrical portion andfirst and second end portions having diameters greater than the centralcylindrical portion. The first and second end portions are disposedproximate opposite ends of the opening and the metal castingsubstantially fills the central cylindrical portion and the first andsecond end portions of the opening whereby the polymeric member isrotatably disposed and axially captured on the metal casting.

The invention comprises, in another thereof, a transmission shiftmechanism for use with a vehicle transmission. The transmission shiftmechanism includes a user-operated selector and a sub-assembly operablydisposed between the user-operated selector and the vehicletransmission. The subassembly includes a polymeric member having anexterior engagement surface engaged with the transmission mechanism. Thesubassembly also includes a unitary metal casting securable to thetransmission shift mechanism. The metal casting is engaged with thepolymeric member and relatively moveably captures the polymeric memberon the metal casting.

The invention comprises, in still another form thereof, a method ofmanufacture. The method includes providing a polymeric member, placingthe polymeric member in a mold, and casting a metal material within themold wherein the cast metal material relatively moveably couples thepolymeric member with the cast metal material.

In some embodiments of the method, the polymeric member is formed byinjection molding. In still other embodiments, the polymeric member isprovided with an opening defining a rotational axis of the polymericmember, the step of casting the metal material rotationally disposes andaxially captures the polymeric member on the metal cast material.Further, the metal cast material and polymeric member are installed in avehicular transmission shift mechanism wherein the metal cast materialis pivotally secured to the transmission shift mechanism and theexterior surface of the polymeric member is engaged with thetransmission mechanism, the rotational axis of the polymeric memberbeing disposed substantially perpendicular to the pivot axis defined bythe metal cast material.

An advantage of the present invention is that it provides a relativelyefficient manufacturing process for creating an assembly having apolymeric member that is moveably coupled with a cast metal member.

Another advantage is that it provides a robust sub-assembly for use in atransmission mechanism that can be relatively inexpensively manufacturedand which facilitates the efficient assembly of the transmission shiftmechanism.

BRIEF DESCRIPTION OF THE DRAWINGS

The above mentioned and other features of this invention, and the mannerof attaining them, will become more apparent and the invention itselfwill be better understood by reference to the following description ofan embodiment of the invention taken in conjunction with theaccompanying drawings, wherein:

FIG. 1 is a view of a portion of a steering column with a transmissionshift mechanism mounted thereon.

FIG. 2 is an enlarged view of a portion of the transmission shiftmechanism shown in FIG. 1.

FIG. 3 is a view of a prior art crank arm for a transmission shiftmechanism.

FIG. 4 is a cross sectional view of the ball portion of the crank arm ofFIG. 3 taken through the center of the ball portion.

FIG. 5 is a view of a crank arm in accordance with the presentinvention.

FIG. 6 is a cross sectional view of the ball portion of the crank arm ofFIG. 5 taken through the center of the ball portion.

FIG. 7 illustrates an alternative embodiment of the crank arm.

FIGS. 8A-8C illustrate an exemplary embodiment of a method ofmanufacture disclosed herein, wherein FIG. 8A is a cross-sectional viewof a die configured to receive a polymeric member and define a moldcavity for molding a metal material, FIG. 8B is a cross-sectional viewof the die of FIG. 8A where the polymeric member has been provided andplaced into the mold cavity of the mold prior to casting the metalmaterial, and FIG. 8C is a cross-sectional view of the die and polymericmember of FIG. 8B after casting of the metal material into the moldcavity and solidification.

Corresponding reference characters indicate corresponding partsthroughout the several views. Although the exemplification set outherein illustrates embodiments of the invention, in several forms, theembodiments disclosed below are not intended to be exhaustive or to beconstrued as limiting the scope of the invention to the precise formsdisclosed.

DETAILED DESCRIPTION

An automatic transmission shift mechanism 20 is depicted in FIGS. 1 and2. shift mechanism 20 includes a driver-operated shift lever 22 forselection of one of the gears or gear arrangements of the automatictransmission, e.g., park-reverse-neutral-drive-low (PRNDL). Lever 22 iscoupled to a rotatable 24 which extends through housing 26 and definesan axis 28. Crank arm 30 is rotatably fixed to shift shaft 26. Movementof lever 22 rotates shift shaft 24 and thereby rotates or pivots crankarm 30 about axis 28 through a defined range of motion.

Crank arm 30 includes a crank arm component 32 and a ball component 34.Crank arm 30 is coupled with actuator 36 via ball component 34. Actuator36 is rotatably attached at pivot point 38 to housing 26 and includes anattachment member 40. A cable or linkage (not shown) is attached at oneend to attachment member 40 and is attached at its other end to the gearselector of a vehicle transmission (not shown).

Actuator 36 also includes an arcuate camming slot 42 in which ballcomponent 34 is disposed. Movement of lever 22 rotates both shift shaft24 and attached crank arm 30 thereby causing ball component 34 to movethrough an arc. As ball component 34 moves, it forcibly engages cammingslot 42 and pivots actuator 36 about its pivot point 38. The pivotingmovement of actuator 36 and attachment 40 results in the changing of thegear of the vehicle transmission via the cable or linkage (not shown)secured to both attachment member 40 and the gear selector of thetransmission (not shown). The illustrated mechanism 20 is mounted on asteering column assembly 44.

Except for crank arm 30, which is discussed in greater detail below, theabove-described operation and structure of shift mechanism 20 is wellknown in the art. FIGS. 3 and 4 illustrate a prior art crank arm 46. Theuse of crank arm 46 with shift mechanism 20 is well known in the art.

Prior art crank arm 46 includes an arm component 48 and a ball component50. Arm component 48 is formed from a steel rod or other suitablematerial in a progressive cold stamping operation and includes a thingenerally planar portion 52. A slug is punched from planar portion 52 toform aperture 54 having flats 56. Shift shaft 24 is inserted throughaperture 54 and engages flats 56 when securing crank arm 46 to shiftmechanism 20. Aperture 54 is provided with a chamfer along its edge onone side of planar portion 52 to ease assembly of the crank arm 46 onthe shift shaft 24. Punch tolerances prevent the chamfer from beingformed on both sides of planar portion 52 and, consequently, crank arm46 must be properly oriented with regard to the single chamfered side ofcrank 46 when securing crank arm 46 to shift shaft 24.

Arm component 48 also includes a generally cylindrical post 58 on whichball component 50 is mounted. Post 58 is inserted through opening 60 inball 50 and its end is staked to secure ball 50 on arm component 48.Ball component is formed by extruding a polymeric material, e.g.,acetal, and then machining the material to form the substantiallyspherical exterior surface 62 and opening 60 of ball 50.

Opening 60 has a central cylindrical section 64 and cylindricalcounterbores 66 at opposite ends of opening 60. The staking operationdeforms the distal end of post 58 such that the deformed portion fillsthe distal counterbore 66 of opening 60 to attach ball component 50 toarm component 48. The staking attachment of ball 50 on post 58 fixesball 50 to post 58 in a manner that does not allow ball to rotate. Themore complex, and thus expensive, use of a shoulder bolt to attach ball50 would allow ball 50 to rotate. In either case, because the rotationalorientation of ball 50 is not controlled during the staking operation,the exterior surface 62 of ball component 50 must be machined to closetolerances for its fill circumference to provide an acceptable level ofrolling or sliding engagement with camming slot 42. Not only must thearm and ball components 48, 50 meet their respective tolerances, but thedeformation and cracking of ball component 50 must be prevented duringthe staking operation. As will be understood by a person having ordinaryskill in the art, the proper operation and durability of shift mechanism20 is highly sensitive to the process by which prior art crank arm 46 ismanufactured and assembled.

Turning now to FIGS. 5 and 6, a crank arm 30 in accordance with thepresent invention is shown in greater detail. Crank arm 30 is anassembly of a metal cast component 32 and a polymeric member 34. Asmentioned above, assembly 30 is a sub-assembly of transmission mechanism20 operably disposed between the user-operated selector 22, which in theembodiment illustrated in Figure is a steering column mounted shiftlever, and actuator 36 which, in turn, is operably coupled to thevehicle transmission (not shown) via a cable or other suitable linkage(not shown).

Polymeric member 34 may be formed out of any suitable plastic materialand, in the illustrated embodiment, is formed by an injection moldingprocess using an acetal material. Advantageously, the polymeric materialused to form member 34 is a self-lubricating material. Self-lubricatingpolymeric materials which may be suitable for one or more of the variousalternative embodiments of the present invention include acetal, nylon,polytetrafluoroethylene (PTFE) available under the trademark Teflon,ultra high molecular weight polyethylene (UHMWPE), and other suitablematerials known to those having ordinary skill in the art.

As best seen in FIG. 6, polymeric member 34 has an exterior engagementsurface 86 which defines a substantially spherical body 34. The shape ofmember 34, however, differs that of a sphere at the opposing ends ofopening 88 which extends through member 34. Opening 88 includes acentral cylindrical portion 90 and first and second end portions 92. Endportions 92 are flared and have a diameter that increases in size as endportions progress radially outwardly the center of polymeric member 34.The diameter of end portions 92 is larger than the diameter of centralportion 90 to provide for the capture of polymeric member 34 on metalcasting 32. Both polymeric member 34 and opening 88 extending throughpolymeric member are symmetric about central axis 94.

Polymeric member 34 is rotationally disposed on metal casting 32 andwhen crank arm 30 is installed in transmission shift mechanism 20,exterior surface 86 is rollingly engaged with actuator 36. In theillustrated embodiment, polymeric member 34 is rotatably disposed innon-linear camming slot 42 with axis 94 defining the rotational axis ofpolymeric member 34.

Polymeric member 34 is captured on unitary metal casting 32 which isbest seen in FIG. 5. As used herein a “unitary” metal casting refers toa metal casting that is formed by cooling a single mass of molten orsemi-molten metal material. Mechanically fastening, welding or adheringto metal castings rigidly together would be an assembly of metalcastings rather than a unitary metal casting. Such a unitary metalcasting could then be rigidly or moveably secured or coupled to othermetallic or non-metallic parts to form a larger assembly orsub-assembly.

In the illustrated embodiment, metal casting 32 is formed out of a zincalloy. Other suitable metal materials, however, may also be used to formmetal casting 32. The illustrated metal casting 32 includes a generallyplanar or flat arm portion 70 and a post portion 72. Arm portion 70defines an aperture 74 having flats 76 and a chamfer 78 along the entireouter circumference of aperture 74 on both sides of arm portion 70.Chamfer 78 facilitates the assembly of metal casting 32 onto shift shaft24 and providing a chamfer 78 on both sides of arm portion 70 eliminatesthe need to directionally position the opposite sides of flat armportion 70 during assembly. Post portion 72 has a shape corresponding toopening 88 with a central cylindrical portion 80, a proximal flaredportion 82 a and a distal flared portion 82 b. A small distalcylindrical portion 84 of post portion 72 projects outwardly fromopening 88 and is an artifact of the manufacturing process.

Flat arm portion 70 is secured to shift mechanism 20 by inserting theend of shift 24 through aperture 74. Flats on shift shaft 24 are engagedwith flats 76 so that crank arm 30 pivots about axis 28 as shift shaft24 is rotated about axis 28 by the movement of shift lever 22. Polymericmember 34 is moveably captured on post portion 72 of metal casting 34and, in the installed position depicted in FIGS. 1 and 2, the pivot axis28 of metal casting 32 is positioned substantially perpendicular to therotational axis 94 of polymeric member 34 defined by opening 88.

In the illustrated embodiment, metal casting 32 substantially fillscylindrical portion 90 and first and second end portions 92 of opening88. As a result, polymeric member 34 is both rotatably disposed on postportion 72 and axially captured between flared portions 82 a and 82 b.Flared portions 82 a, 82 b are located proximate opposite ends ofopening 88 with distal flared portion 82 b preventing thenon-destructive removal of polymeric member 34 from metal casting 34.Distal flared portion 82 b thereby captures polymeric member 34 on metalcasting 32.

An alternative configuration of the interface between the metal castingand polymeric member is illustrated in FIG. 7. In the embodiment 30 a ofFIG. 7, polymeric member 34 a (shown in dashed outline) is rotatablydisposed and axially captured on a post portion 72 a of a metal casting.Assembly 30 a can be used in transmission shift mechanism 20 andfunctions the same as assembly 30 in mechanism 20. Polymeric member 34 aincludes a cylindrical opening that extends through the center of thegenerally spherical polymeric member 34 a and has an enlarged diameterportion proximate the center of the polymeric member 34 a. Thecorresponding casting substantially fills the opening in polymericmember 34 a and includes a proximal cylindrical portion 80 a, a distalcylindrical portion 80 b and an enlarged diameter portion 82 c having arounded profile. The rotatable bearing engagement between the polymericmember and the metal casting is facilitated by the use of cylindricalportions 80 a, 80 b. Enlarged diameter portion 82 c axially capturespolymeric member 34 a on the metal casting and in further modificationsof the assembly may take different shapes including a generallyspherical shape or a cylindrical disk shape. Polymeric member 34 a maybe formed by injection molding to define the exterior shape and centralcylindrical opening of member 34 a with the enlarged diameter portion ofthe opening being machined in polymeric member 34 a subsequent to theinjection molding process and prior to the casting of the metalmaterial. The use of an enlarged diameter portion 82 c in a centrallocation of the opening in polymeric member 34 a allows the singleenlarged diameter portion 82 c to axially capture polymeric member 34 aon the metal casting. Although illustrated capturing elements 82 a, 82 band 82 c are all located within an opening in a polymeric member, thisis not a requirement. For example, if flared portions 82 a and 82 b werereplaced by an extension of cylindrical portion 80 in assembly 30,distal portion 84 could be diametrically enlarged to thereby capturepolymeric member 34 on metal casting 34 between portion 84 and flat armportion 70 both of which would bear against the exterior surface ofpolymeric member 34 proximate opposite ends opening 88 to prevent thenon-destructive removal of polymeric member 34 from metal casting 32,

Various other configurations of opening 88 and post portion 72 may alsobe used to moveably capture polymeric member 34 on metal casting 32. Forexample, in alternative applications, it might be desirable to elongatethe distance between flared 82 a, 82 b to allow polymeric member 34 toboth rotate and slide on post portion 72. In yet other applications,opening 88 and an elongated central portion 80 of post portion 72 couldbe provided with similar non-circular cross-sections to non-rotatablyand slidably capture polymeric member 34 on metal casting 32.

Assembly 30 can be manufactured in a relatively inexpensive andefficient manner. In the illustrated embodiment, polymeric member 34 isan actual material and is formed using a conventional injection moldingprocess. Polymeric member 34 does not require any machining after beingformed by the injection molding process. In other words, theconfiguration of polymeric member 34 when it is installed intransmission shift mechanism 20 is substantially the same as theconfiguration of polymeric member 34 produced by the injection moldingprocess.

Polymeric member 34 a is also formed using an injection molding process,however, it is subject to a later machining operation to form a grooveto receive and define enlarged diameter portion 82 c of the metalcasting. Although polymeric member 34 a does not totally eliminate theuse of machining processes to form member 34 a, the ability tomanufacture member 34 a by an injection molding process followed by onlyminimal machining provides a significant cost savings when compared tothe much greater machining required to form a similar member from anextruded material.

The use of an injection molding process is facilitated by rotatablymounting polymeric member 34 on metal casting 32. This rotatablemounting of polymeric member 34 on metal casting 32, allows polymericmember 34 to rotate within camming slot 42 and thereby be in rollingengagement with camming slot 42 as metal casting 32 is pivoted. Incontrast, a non-rotatably fixed ball component 50 will slide withincamming slot 42. The sliding engagement of ball component 50 createshigher stresses within ball component 50 than the stresses created bythe rolling engagement of polymeric member 34. To satisfy these strengthdemands, ball component 50 is formed by extruding an acetal material andthen machining the material to form ball component 50. This extrusionand machining process produces a ball component with greater internalstrength proximate exterior surface 62 than an injection molding processbecause of the effects of differential cooling that accompany the use ofan injection molding process when forming an article having the shape ofball component 50. Generally, the injection molding of a part having thegeneral shape of either ball component 50 or polymeric member 34 willresult in a part that has its greatest material strength properties atits core and has its weakest properties at its exterior surface.

The use of an injection molding process to form a ball component 50 thatcannot rotate about post 58 and must slide against camming slot 42 maylead to an unacceptably high failure rate of ball component 50. Byrotatably mounting polymeric member 34 on metal casting 32 and allowingpolymeric member 34 to rollingly engage camming slot 42, the stressesimposed on polymeric member 34 are reduced sufficiently to enable theuse of an injection molded part. As described above, the ability to usean injection molded part is advantageous because it is considerably lessexpensive to form polymeric member 34 by injection molding than to formball component 50 by an extrusion and machining process. Additionally,the use of a rotatable polymeric member 34 in shift mechanism 20 isadvantageous because it reduces wear on polymeric member 34, reduces thedrag and shifting effort thereby providing an improved feel, andprovides a greater range of material and manufacturing options forproducing polymeric member 34.

After forming polymeric member 34 with opening 88 therein, polymericmember 34 is placed (FIG. 8B) in a mold 100, e.g., a die (FIG. 8A)having a mold cavity 102 configured to form the crank arm 30 (FIG. 5). Amolten or semi-molten metal material is then introduced into the mold100 and allowed to cool to thereby form metal casting 32. When themolten metal material is introduced into the mold 100 through an opening104 into the mold cavity 102, it fills opening 88 to couple theresulting metal casting 32 with polymeric member 34. As the molten metalmaterial cools to form metal casting 32 (FIG. 8C), it shrinks therebyproviding the clearance between post portion 72 and opening 88 necessaryto allow polymeric member 34 to rotate on post portion 72.

The illustrated embodiment employs a zinc alloy to form metal casting 32with an acetal member 34 to provide an acceptable clearance betweenmetal casting 32 and polymeric member 34 to rotatably capture member 34on casting 32. The zinc die casting alloy used to form metal casting 32is advantageously ACuZinc, a zinc alloy that has a relatively lowcoefficient of friction. The casting of the metal material to formcasting 32 may be done in Injected Metal Assembly (IMA™) equipmentavailable from Fisher Cast Global Corporation having a place of businessat 310 Armour Road, Peterborough, Ontario, Canada K9J 6Y9. The quickcycle times obtainable with the use of a zinc alloy in such a processpermits the forming of metal casting 32 without impairing thefunctionality of the polymeric member.

The use of a die casting process to metal casting 32 eliminates the needto use a machining, stamping or cold forming process in the manufactureof metal casting 32. Not only does the use of die casting eliminate theneed to use such processes to form the general shape of metal casting32, but no machining, stamping or cold forming process is required aftermetal casting 32 is removed from the die. In other words, metal casting32 can be installed in transmission shift mechanism 20 in substantiallythe same configuration as when it was removed from the die. It alsoprovides a wide range of shape options for metal casting 32. Forexample, die casting metal component 32 facilitates the use of acomponent 32 which has a symmetrical design thereby facilitating theinstallation of the metal casting into a larger assembly. Machined andotherwise manufactured parts can also be provided in symmetrical shapes,however the designer will often be confronted with the trade-off betweenmachining both sides of a part or machining a single side and requiringthe part to be positionally oriented when installing it in a largerassembly. Additionally, the corners and transitions of a die cast partcan often be shaped to reduce the stress concentrations at such pointsin comparison to parts formed by machining, stamping or similarprocesses.

While this invention has been described as having an exemplary design,the present invention may be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles.

What is claimed is:
 1. An assembly comprising: a polymeric member; and aunitary metal casting, said metal casting engaged with and relativelymoveably capturing said polymeric member on said metal casting, saidpolymeric member including an opening extending through said polymericmember, said opening defining a rotational axis of said polymeric memberand including a central cylindrical portion and first and second endportions having diameters greater than said central cylindrical portion,said first and second end portions being disposed proximate oppositeends of said opening, and wherein said metal casting substantially fillssaid central cylindrical portion and said first and second end portionsof said opening, thereby rotatably disposing and axially capturing saidpolymeric member on said metal casting.
 2. The assembly of claim 1,wherein the polymeric member has a substantially spherical exteriorsurface.
 3. The assembly of claim 2, wherein the first end portion andthe second end portion of the opening each taper inwardly from theexterior surface toward a center of the polymeric member.
 4. Theassembly of claim 1, wherein said polymeric member comprises aself-lubricating polymeric material.
 5. The assembly of claim 1, whereinsaid polymeric member comprises an acetal material.
 6. The assembly ofclaim 1, wherein said unitary metal casting comprises a crank arm. 7.The assembly of claim 6, wherein said crank arm comprises a generallyplanar arm portion and a post portion, said post portion engaged withand relatively moveably and axially capturing said polymeric member onsaid post portion.
 8. The assembly of claim 7, wherein said generallyplanar arm portion comprises an aperture.
 9. The assembly of claim 8,wherein said generally planar arm portion comprises a first side and asecond side, and said aperture has a chamfer surrounding said apertureon each of said first side and said second side.
 10. The assembly ofclaim 1, wherein said unitary metal casting comprises a zinc alloy. 11.A transmission shift mechanism for use with a vehicle transmissioncomprising: a user-operated selector; and a sub-assembly operablydisposed between said user-operated selector and the vehicletransmission, said sub-assembly including: a polymeric member having anexterior engagement surface engaged with said transmission shiftmechanism; and a unitary metal casting, said metal casting engaged withsaid polymeric member and relatively moveably capturing said polymericmember on said metal casting, said casting being secured to saidtransmission shift mechanism, said polymeric member including an openingdefining a rotational axis of said polymeric member and said openingincludes a central cylindrical portion and first and second end portionshaving diameters greater than said central cylindrical portion, saidfirst and second end portions being disposed proximate opposite ends ofsaid opening, said metal casting substantially filling said centralcylindrical portion and said first and second end portions of saidopening thereby rotationally disposing and axially capturing saidpolymeric member on said metal casting.
 12. The assembly of claim 11,wherein the polymeric member has a substantially spherical exteriorsurface.
 13. The assembly of claim 12, wherein the first end portion andthe second end portion of the opening each taper inwardly from theexterior surface toward a center of the polymeric member.
 14. Theassembly of claim 11, wherein said polymeric member comprises aself-lubricating polymeric material.
 15. The assembly of claim 11,wherein said polymeric member is rotatably disposed within a non-linearcamming slot defined by said transmission shift mechanism. saidpolymeric member comprises an acetal material.
 16. The assembly of claim11, wherein said unitary metal casting comprises a crank arm.
 17. Theassembly of claim 16, wherein said crank arm comprises a generallyplanar arm portion and a post portion, said post portion engaged withand relatively moveably and axially capturing said polymeric member onsaid post portion.
 18. The assembly of claim 17, wherein said generallyplanar arm portion comprises an aperture, and wherein said generallyplanar portion is pivotally secured through said aperture to thetransmission shift mechanism about a pivot axis disposed substantiallyperpendicular to said rotational axis of said polymeric member.
 19. Theassembly of claim 18, wherein said generally planar arm portioncomprises a first side and a second side, and said aperture has achamfer surrounding said aperture on each of said first side and saidsecond side.
 20. The assembly of claim 11, wherein said unitary metalcasting comprises a zinc alloy.